Can fish introductions alter nutrient cycles in previously fishless high-latitude lakes?

• Published in: Journal of Limnology
• Main Authors: Marco Milardi, Jyrki Lappalainen, Suzanne McGowan, Jan Weckstrom
• Format: Article in Journal/Newspaper
• Language: English
• Published: PAGEPress Publications 2016
• Subjects: nutrient cycle; bioenergetic model; fish introduction; chlorophyll and carotenoid pigments; diatoms; stable isotopes; envir; geo; Boreal Lake; Fennoscandia
• Online Access: https://doi.org/10.4081/jlimnol.2016.1364; https://doaj.org/article/fc0b1cef1d8e40f08641064dcf0a5304

The additional input and enhanced cycling of nutrients derived from introduced fish can be a significant factor altering nutrient dynamics in oligotrophic lakes. To test this, we used a bioenergetic model to estimate the fish-derived nutrient load in Lake Kuutsjärvi, a historically fishless boreal lake of northern Fennoscandia. The lake was selected because of the absence of other anthropogenic stressors, a known stocking history and the possibility of quantitatively estimating the size-structure and biomass of the fish population through a mass removal. Subsequently, we used a mass balance model to compare fish-derived nutrients with other nutrient load pathways. For comparison over longer timescales, we used lake sediment records of diatoms, chlorophyll and carotenoid pigments, C:N ratios and stable isotopes to infer whether fish introduction produced detectable changes in the lake trophic state, primary productivity and terrestrial nutrient input. Based on the nutrient mass balance model, we found that phosphorus and nitrogen derived from fish were 0.46% and 2.2%, respectively, of the total load to the lake, suggesting that fish introduction could not markedly increase the nutrient load. Accordingly, the palaeolimnological record indicated little increase in primary production but instead a shift from pelagic to benthic production after fish introduction.